Theresa May will on Wednesday become the politician tasked with leading Britain into talks to leave the EU after her only rival in the race to succeed Prime Minister David Cameron pulled out unexpectedly.

Leadsom and May square off for British PM job

May was left as the only contender standing after the withdrawal from the Conservative Party leadership race of Andrea Leadsom, who faced criticism for suggesting she was more qualified to be prime minister because she had children.

“I am honoured and humbled to have been chosen by the Conservative Party to become its leader,” said May in London after she was formally confirmed as the winner of the Conservative leadership contest on Monday afternoon.

“During this campaign, my case has been based on three things. First, the need for strong, proven leadership to steer us through what will be difficult and uncertain economic and political times; the need to negotiate the best deal for Britain in leaving the EU; and to forge a new role for ourselves in the world.”

Cameron said he would resign as prime minister on Wednesday, paving the way for May to take over the job the same day.

He said he expected to chair his last cabinet meeting on Tuesday, and then take questions in parliament for around 30 minutes from 11:00 GMT on Wednesday.

"After that I expect to go to [Buckingham Palace] and offer my resignation," he told reporters outside his office in Downing Street. "So we will have a new prime minister in that building behind me by Wednesday evening."

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Al Jazeera's Paul Brennan, reporting from London, said May was the choice of many in the ruling party.

"Of the five people that contested the Conservative Party leadership, many people regarded Theresa May as perhaps the more establishment figure. She has been the home secretary, the interior minister, for the past six years and because of that she has had intimate knowledge of the workings of the government and has had to liaise very closely with her European counterparts on matters of security and immigration," Brennan said.

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"She has much less of a track record in relation to the economics of European Union, and certainly the issue of Britain divorcing itself from the EU is going to be an issue that she is going to have to come to speed with very quickly," he added.   

Britain has faced the worst political turmoil in generations following June 23's shock vote to leave the European Union, which prompted Cameron to step down.

His party has endured a bitter leadership race, while the leader of the main opposition Labour Party, Jeremy Corbyn, is also facing a challenge to his job.

While May supported Britain staying in the EU, she cut a low profile during the referendum and has insisted she will honour the vote.

“Brexit means Brexit and we are going to make a success of it," May said on Monday.

"We need to unite our country ... we need a strong new positive vision for the future of our country, a vision of a country that works not for the privileged few, but that works for every one of us because we’re going to give people more control over their lives. And that’s how, together, we will build a better Britain."

May wants to begin formal talks to leave the EU by the end of the year at the earliest, despite pressure from Brussels to speed up.

Jeroen Dijsselbloem, the Dutch finance minister who heads the Eurogroup of his 19 eurozone counterparts, restated calls for the transfer of power to take place as soon as possible.

"The sooner we can sort out - let me say it diplomatically - this problematic situation, the better," Dijsselbloem told reporters.

General election call

The pound, which hit a 31-year low in the wake of the Brexit vote, briefly rose after Leadsom, a pro-Brexit figure with no senior ministerial experience, withdrew from contention to be prime minister.

As senior MP Angela Eagle formally launched her leadership challenge against Corbyn, Labour suggested a general election would need to be held soon after May takes office.

"It is crucial, given the instability caused by the Brexit vote, that the country has a democratically elected prime minister," said election coordinator Jon Trickett.

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"I am now putting the whole of the party on a general election footing."

May, a 59-year-old clergyman's daughter, will be Britain's second female prime minister after Margaret Thatcher, who was in office from 1979 to 1990.

She has portrayed herself as the leader who can unite the country following a bitterly divisive campaign, and a tough negotiator who can stand up to Brussels in what promise to be tortuous talks over Britain's exit from the European Union.

Leadsom's withdrawal means all the top Brexit campaigners - Boris Johnson, Michael Gove, Leadsom and outgoing UK Independence Party leader Nigel Farage - have now stepped back from leadership roles.

"Brexiteers threw rocks through the window, now they're all running away from the house," author Salman Rushdie said on Twitter.

'Howl of pain'

On the latest in a string of astonishing days at Westminster recently, Eagle also launched her bid to take over the leadership of the main opposition Labour Party from veteran socialist Corbyn.

Corbyn has widespread support among party members but has lost the confidence of at least three-quarters of his MPs, many of whom accuse him of lacklustre campaigning to stay in the EU.

Eagle, who is from Labour's "soft" left and was the first female MP to enter a civil partnership with her female partner in 2008, said Britain faced "dangerous times".

Of the referendum, she added: "This vote was a message for millions in our country who felt that no one had listened to them for a very long time.

"For many of them, it was a howl of pain."

By contrast with the Conservative outcome, there is still major uncertainty about how the Labour leadership contest will work out.

Central to the race will be a decision by Labour's governing National Executive Committee (NEC) about whether Corbyn automatically gets on to the ballot or needs to secure 51 lawmakers' nominations, which he could struggle to do.

The NEC is due to meet on Tuesday.

Source: Al Jazeera and agencies